Allen-Bradley 1791-0A16: Legacy AC Output Block I/O Module

Control AC devices directly from your classic PLC system. The Allen-Bradley 1791-0A16 is a sixteen-channel AC output module from the Block I/O series. It operates on 20-132V AC to drive industrial loads like contactors, pilot lights, and alarms. This module is designed for distributed I/O applications with legacy PLC-2, PLC-3, and PLC-5 controllers.

Detailed Technical Specifications

• Product Model: Allen-Bradley 1791-0A16 (1791 Block I/O Series).
• Output Configuration: 16 AC output channels in 2 groups of 8.
• Voltage & Frequency: 20-132V AC, 47-63 Hz (120V AC nominal).
• Current Rating (Vertical Mount): Up to 600 mA total @ 30°C, 300 mA @ 60°C.
• Switching Details: 50 mA per output max, 10A surge current for 50 ms.
• Response Time: Turn-ON delay 1.0 ms, Turn-OFF delay 8.3 ms @ 60 Hz.
• External Power: Requires 85-132V AC, 47-63 Hz supply (150 mA continuous).
• Isolation Ratings: 500V AC (Power to RIO), 1250V AC (I/O group to group & group to logic).

Installation & Wiring Information

• Mounting Orientation: Supports both vertical and horizontal mounting (current rating varies).
• Wiring: Removable terminal strip for convenient connection; use 14 AWG stranded wire max.
• Thermal Derating: Output current capacity decreases with higher ambient temperature.
• Status Indication: Integrated status LED for module diagnostics and troubleshooting.
• Module Weight: 1.19 lbs (0.54 kg).

Packaging & Support Details

• Package includes one 1791-0A16 AC output module.
• This legacy product is supplied for system maintenance and repair.
• We ship worldwide using reliable carriers like FedEx, UPS, and DHL.

Expert FAQs

• What is the primary use case for this module today?
  It is primarily used for maintaining and servicing existing installations that use PLC-2, PLC-3, or PLC-5 controllers on a Remote I/O network. It's a spare part for legacy systems still in operation.
• Why does the current rating change with mounting orientation?
  Heat dissipation. When mounted vertically, convection airflow is better, allowing higher continuous current. Horizontal mounting restricts airflow, requiring derating to prevent overheating.
• Can I use this module to directly control a motor starter coil?
  Yes, if the coil voltage is within 20-132V AC and the inrush/steady-state current is within the module's ratings. A typical small contactor coil (120V AC, ~10VA) draws about 80 mA, which is within one channel's 50 mA limit, but check your specific device.
• What does the "10A surge current" specification mean?
  The output can withstand a brief high-current inrush, such as when energizing a lamp (cold filament) or a contactor coil, for up to 50 milliseconds. This is crucial for reliable switching of real-world inductive and incandescent loads.
• How do I integrate this with a modern ControlLogix or CompactLogix system?
  You cannot connect it directly. You would need a legacy communication bridge (like a 1785-BCM) to connect the Remote I/O network to a modern controller's backplane, or replace the entire I/O system with a modern platform like Point I/O or CompactBlock.

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